Our laboratory has been actively studying the pathogenesis of alcoholic liver disease, focusing on how alcohol attenuates T-cell metabolism and hepatitis in ALDH2-deficient mice and humans. Alcohol inhibits T-cell glucose metabolism and hepatitis in ALDH2-deficient mice and humans: Roles of acetaldehyde and glucocorticoids Objective: Aldehyde dehydrogenase 2 (ALDH2), a key enzyme to detoxify acetaldehyde in the liver, exists in both active and inactive forms in humans. Individuals with inactive ALDH2 accumulate acetaldehyde after alcohol consumption. However, how acetaldehyde affects T-cell hepatitis remains unknown. Design: Wild-type and Aldh2-/- mice were subjected to chronic ethanol feeding and concanavalin A (ConA)-induced T-cell hepatitis. Effects of acetaldehyde on T-cell glucose metabolism were investigated in vitro. Human subjects were recruited for acute alcohol drinking and plasma cortisol and corticosterone measurement. Results: Ethanol feeding exacerbated ConA-induced hepatitis in wild-type mice but surprisingly attenuated it in Aldh2-/- mice despite higher acetaldehyde levels in Aldh2-/- mice. Elevation of serum cytokines and their downstream signals in the liver post ConA injection was attenuated in ethanol-fed Aldh2-/- mice compared to wild-type mice. In vitro exposure to acetaldehyde inhibited ConA-induced production of several cytokines without affecting their mRNAs in mouse splenocytes. Acetaldehyde also attenuated IFN- production in phytohemagglutinin-stimulated human peripheral lymphocytes. Mechanistically, acetaldehyde interfered with glucose metabolism in T cells by inhibiting aerobic glycolysis-related signal pathways. Finally, compared to wild-type mice, ethanol-fed Aldh2-/- mice had higher levels of serum corticosterone, a well-known factor that inhibits aerobic glycolysis. Blockade of corticosterone partially restored ConA-mediated hepatitis in ethanol-fed Aldh2-/- mice. Acute alcohol drinking elevated plasma cortisol and corticosterone levels in human subjects with higher levels in those with inactive ALDH2 than those with active ALDH2. Conclusions: ALDH2 deficiency is associated with elevated acetaldehyde and glucocorticoids post alcohol consumption, thereby inhibiting T-cell activation and hepatitis